1. Field of the Invention
This invention relates to valve apparatus and, more particularly, to valve apparatus for controlling the flow of irrigation water from an irrigation water line.
2. Description of the Prior Art
The proper utilization of the water for the irrigation of agricultural crops has been of increasing concern for a number of years for several different reasons. One reason is the consideration of water, itself. For example, in many parts of the country, particularly the southwest, the ground water table is lowering as water is pumped from the underground aquafers and reservoirs faster than it is being replenished by nature. Another reason of substantial importance is the effect of water in varying amounts on growing crops. While the effects of too little water are well known, it has been only recently that scientific studies have determined that there may be an optimum amount of water for a given crop, and that water in excess of the optimum amount of water is literally wasted. If, therefore, depending on the soil conditions and on the particular crop being watered, the optimum amount of water is available, maximum yield may be obtained.
In an effort to improve the efficiency of irrigation, the so-called "dead level" or basin irrigation system has been developed in recent years. To prevent pooling in low areas and runoff from higher areas, fields are leveled using the most efficient and accurate contemporary methods, such as laser controlled levelling techniques.
In order to provide the proper amount of water for field crops for irrigation purposes, valves are located periodically along water lines extending in the fields. Valves are actuated to allow water to flow onto the fields, thus providing the necessary irrigation water.
U.S. Pat. No. 946,516 discloses a hand-operated irrigation valve for controlling the flow of water from a closed conduit.
U.S. Pat. No. 1,960,284 discloses a valve controlled by changes of pressure in the fluid system. The internal pressure is utilized to control flow through the valve, with changes in the upstream pressure and downstream pressure being used to actuate the valve.
U.S. Pat. No. 2,243,711 discloses an air loaded relief valve which utilizes a pair of pistons secured to a common shaft. The pistons each have different diameters.
U.S. Pat. No. 2,646,076 disloses a manually operated piston movable to control fluid flow in an irrigation system.
U.S. Pat. No. 2,696,361 discloses a spring loaded valve held closed by the spring. Air acting on the bottom of a piston opens the valve when the air pressure overcomes the bias of the spring holding the valve closed.
U.S. Pat. No. 2,778,598 discloses valve apparatus actuated by pressure acting on one side of a piston. Pressure on the opposite side of the piston closes the valve against the pressure of the fluid flowing through a conduit. The pressure of the fluid flowing through the conduit accordingly causes the valve to open when the fluid pressure exceeds the control pressure on the opposite side of the piston. A double piston arrangement is also used.
U.S. Pat. No. 3,251,377 discloses a diaphragm used to control a valve by pressure applied to one side of the diaphragm. The pressure causes a valve member secured to the diaphragm to close. Reducing pressure on the diaphragm allows pressure of the fluid in the system to open the valve.
U.S. Pat. No. 3,552,658 discloses another piston and cylinder arrangement in which a spring is used to secure a piston to a cylinder head, and the spring provides a bias against the piston to open the valve. The valve is closed against the spring bias by air pressure acting on the piston.
U.S. Pat. No. 4,031,915 discloses a valve arrangement for an irrigation system which includes a plurality of drip tubes connected to a pressurized water supply. A valve element is freely movable within a cylinder in response to pressure differences, and pressure on one side of the valve is used to control the position of the valve to regulate the flow of water through the drip tubes. The valve comprises a piston moved in its cylinder by the force of the pressurized water on one side of the piston as against the force or pressure of the irrigation water on the opposite side of the piston.